Secondary seal for floating tank roof



Jan. 26, 1965 w. R NELSON SECONDARY SEAL FOR FLOATING TANK ROOF FiledSept. 17, 1962 United States Patent 3,167 ,206 SECONDARY SEAL FORFLOATING TANK ROOF I William R. Nelson, Houston, Tex., assignor to TheTexas Pipe Line Company, Houston, Tex., a corporation of This inventionrelates generally to liquid storage tanks having floating roofs andparticularly to the secondary seal for the space between the floatingroof and the inner tank wall.

Many oil storage tanks require a floating roof cover of the pontoon typewhich is capable of moving up and down within the tank in accordancewith changes in fluid level as the volume of the tank contents varies.

Sealing structures to close the annular area between the inner wallsurface of the tank and the floating roof usually include a primary sealcomprising a plurality of shoes supported by the floating roof itself,with the open space between the primary seal and the floating roof beingclosed by a continuous flexible fabric seal usually.

Even though the shoes are held against the inner wall surface of thetank with pressure, it is not always possible to hold them in aseal-tight condition so that water and other contaminants will not seepinto the tank through the clearance between the shoes and the wall andbecome admixed with the stored product. Furthermore, there is a problemof corrosion arising in the areas contacted by the shoes of the primaryseal and in case of severe weather,

liquids may freeze between the primary seal shoes and the tank wall.

Accordingly, it is an object of the invention to provide an improvedfloating roof seal which will prevent or minimize the flow ofcontaminants across the seal contact area into the tank.

Another object of the invention is to provide a simple floating roofseal which is economical with respect to the cost of material and thelabor for its installation.

Still another object of the invention is to provide a secondary seal fora floating tank roof which is simple and inexpensive to make and withouta requirement for separate and special support therefor.

Another object of this invention is to provide a novel secondary sealfor a floating tank roof which is in contact with the tank wall at alltimes.

These and other objects, features and advantages of the presentinvention will become apparent from the following description and claimof the present invention when read in the light of the drawing in which:

FIG. 1 is a perspective view of a cross section of a floating tank roofshowing the primary and secondary seals;

FIG. 2 is a cross sectional view of the improved secondary seal;

FIG. 3 is a partial, cross sectional view of the secondary seal shown inoperative position; and

FIG. 4 is a fragmentary view showing an alternate means of fastening thesecondary seal to the edge of the primary seal.

The objects of the present invention are achieved by the application ofa flexible seal directly to the primary seal of a floating tank roof,without the requirement of a special support for the secondary seal, andwhich will be held at all times in sealing position against the tankwall.

Referring to the drawing, part of a cylindrical, open end storage tank,indicated generally at 10, is shown, including the upstanding side wall11 and the floating pontoon type cover or roof 12. The floating roof 12comprises the top deck 13, the bottom deck 14, interconnected "ice bythe rim plate at 15 and bulk heads, one of which is shown at 15a.

The primary seal 16 comprises a number of shoes, such as indicated at16a, each of which is supported by and interconnected with the floatingroof by means of the hanger structure indicated generally at 17. By anappropriate balance of the hanger, 17a, the shoes of the primary sealare held in contact with the inner surface of the tank side wall as thefloating roof rises and falls in accordance with changes in the amountof the contents stored in the tank.

To close the annular space between the floating roof and the shoes ofthe primary seal, a continuous flexible seal, 18, for example, fabric,is fastened to the roof and to the primary seal at 18a and 18brespectively, by means of backing strips and bolts. Conventionalgrounding straps between the floating roof and the primary seal areindicated at 19. Seals and interconnections between each of the shoesare in a manner well known in the art and are not described here.

With respect to the edge structure of each of the shoes of the primaryseal, there is disclosed at 16b an inwardly turned edge or flangeportion angled approximately at 45 and about /2 inch in extent. On thisinwardly turned flange portion or break, a secondary seal 20 ispositioned, the seal having a slot or recess for fitting over the breakin the shoe for support thereby.

Refering in detail to FIG. 2, there is shown a cross section of theresilient secondary seal of a flexible plastic material, e.g. syntheticrubber resistant to hydrocarbon attack and tendency to set, comprisingthe offset contact end portion at 21, the enlarged olfset supportportion at 22, and the planar intermediate interconnecting portion at23. The contact end portion is shown slightly offset and projecting outof the plane of the back or inner surface of the intermediate portionand having a sharp contact edge, but other configurations can be usedfor this contact end portion to compensate for wear, and to insuresuflicient pressure against the inner tank wall surface.

The offset support portion 22 is shown as ending in a substantiallyhemispherical cross section, as indicated at 22a, with a recess 22bextending from the edge of the hemispherical surface inwardly at anangle such that the axis of this recess intersects the axis of thestraight uniform section of the intermediate portion 23 at an obtuseangle X of slightly less than so that when the secondary seal is placedon the 45 break of the upper edge of the shoes of the primary seal at1612, the divergence in angularities will allow adequate contact surfacebetween the contact end portion of the secondary seal and the inner wallsurface. 1

To provide a more positive contact with and to insure pressure on theinner wall surface, use is made of external positioned metallicstiffeners or inserts. On the outer exposed surface 24 of theintermediate portion 23, there are provided tongue-like members 25, 26,projecting toward each other to define grooves 25a, 26a, facing eachother. Into these grooves, metallic stiifeners or inserts 27 are cuppedand seated, the length of each stiffener in the radial direction beingslightly greater than the distance between the bottoms of the facinggrooves 25a, 26a, so that the force exerted by the spring action of thestifleners in a radial direction provides pressure and results in morepositive contact with the inner wall surface of the tank. These externalpositioned inserts are flat sheet metal, e.g. spring bronze strips,about 6 in width, and are spaced circumferentially about A2" apart inthe grooves to act as radial springs. In view of the substantially largediameter of the storage tank in which the secondary seal is to be used,and with the flexibility of the -not only provides an effective seal tominimize or prevent theflow of"c'ontaminants' across the seal into thetank itself, but the configuration of the downwardly directed 'shape of'the secondary seal is .such'that the rain'water runs 'off't'oward'thecenter of the tank roof, whence it' is removed in a manner well knownin the art.

In use, it'hasbeen found most expedient to prepare for 'the applicationof theimproved' secondary seal by cleaning theupperedgesor' breaks ofthe shoesof the primary seal by' scraping and wire brushing, followed'by scrubbing 'witha s'iiitable'solvent' to remove 'paraflin or oil,deposits.

A thin film of a rubber. cement or other rubber adhesive 'is' appliedto'bo'th sides and the edge of'ea ch' break for use as a lubricant inforcing'on the secondary seal and for'bonding the seal to the shoe. Tocomplete the joint between individual SO'Lsections of 'the-:secor1daryseal,

tapes Well known in the art are useda'n'd span the joint adequately; Inaddition, when conditions require I to secure the secondary sealpositively, fastening pins or self tapping screws, appropriately spaced,-'are used as indicated at 40, FIG. 4. f V 7 "Since the secondary sealwill'be .made'of rubber and "most likely from synthetic resilie'ntmaterials which are "not subject to deterioration'either by contactwithhydrocarbon vapors orto abrasion and excessive wear as the seal rubsagainst the'innerjtank fwall, andfeven though the shoes of the. primaryseal rnay'be deflected from the shell by weld seams or deformations ofthe tankwall, the secondary seal has 'sufiicient flexibility andelasticity to bridge the maximum observed deflection of the shoes fromthetank wall. The close contact "of' the secondaryseal with the tank'wall surface preventsfthe escape of'oil or other volatile productvapors from the storage tank while preventing contaminants' from'f'entering thetank across,

the face of the primary seal. Thus there'hasb'een shown'that thesecondary seal of "the type shown herein can be used to aumentetf'ective- 1y 'the'prirnar'y seal of a'fioating roof'of a" storage tank7 in order to retain vaporsfr'o'm'the liquid contents thereof whilepreventing the entrance of contaminants thereinto.

' .Qther modifications and variations of" the invention,

as hereinbefo're setforth, may'be made without departing fronithe spiritand scope thereof, and therefore only 'suchllimitiations should beimposed as are indicated in the appended claim, I

I claim:

, a wardly and downwardly in said container corresponding f to changesin'the' volume of the fiuidihel'd in said container comprising afioating'roof, a primary seal having a plurality of shoes'supported incontact position with the inside wall surface of said container by saidfloating roof --and being spaced annularly therefrom, each ofsaid.plurality of shoes having its top edge projecting angulary away fromsaid inside wall surface, "flexible interconnecting means for closingthe annular opening between said 10 primary seal andrsaidfloatingroofpand a secondary seal aliixed 'on the top edges of said plurality ofshoes of said primary seal and contacting said inside wall surface onits inner protected face with respect thereto, comprisingaiflexiblefangular member having an inside tank Wall "surface contactportion at one; end thereof and" an offset 7 support portion at theother end thereofwith a recess therein, and arr-intermediate portioninterconnecting said contact portionwith said support portionjthe axisof said "recess-in said oifet portion and the axis of said intermediateportion intersecting at 'an' 'obtuse-angle' facing said -in- 'side wallsurface-said" recess insaidsupport portion hav- "mg-dimensionsfor-atightfit-onsaid top edges of said shoes, *deep. enough for adequateengagement with said topedges-bf said shoesand shallow enough to preventcontact' be said support portion with said inside wall surface, said",intermediate portion having *tongue-like'mem- "bers projecting towardeach other thereby'defining a pair of grooves-facing each other 'ontheouterexposed face thereof with respecttosaid inside wall surface, saidtongue like members extending longitudinally of said "secondary"-sealadjacent the support and contact portions "thereof, and a plurality orresilient metallic inserts seated 'in' closely spaced circumferentialrelationship in said pair of grooves; said -inserts having a transversedimension "greater than'the-fdistance between the'bottoms of said pairof grooves whereby a spring action of the inserts in 'a'radial directionisprovided ar'oun'd sai'doffset support portion-to maintain" saidcontact portion of said secondary seal-in positivecontact-withsaidinside tankv Wall 40 surface.

R'efei-en'ces Cit'ed inthe file of this patent 5 UNITED :STATES PATENTS2,259,185 Swedman Oct. 14, 1941 2,287,211 'Wiggins June 23, 19422,348,379 Gouloo ze -May 9, 1944 2,568,728 Goldsby etal. ..Sept. 25,1951 ;-2,'897,998 Ulm n. Aug. 4, 1959 0 2,973,113 Fino Feb. '28, 1961

